New World Screwworm: Need to Know

New World Screwworm (NWS) is a dangerous parasite that affects animals — and sometimes even humans. It’s caused by the larva of a fly (Cochliomyia hominivorax) that lays eggs on or near open wounds. These eggs hatch into maggots that burrow into the flesh and feed on healthy tissue.​

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WHAT ANIMALS ARE AT RISK?

 

Any warm-blooded animal — including livestock, pets, wildlife, and even people — can be affected. Commonly impacted animals include:

• Cattle

• Horses

• Sheep and goats

• Dogs and cats

• Wildlife and birds

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HOW TO SPOT IT

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• Look for maggots in or around a wound

• Look for a wound that’s not healing or getting worse

• Foul smell or tissue damage

If you see maggots, do not wait. This is a serious issue and can quickly lead to death if untreated.

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WHAT TO DO IF YOU SUSPECT NEW WORLD SCREWWORM

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1. Collect a sample using tweezers or forceps. Gently remove larvae from deep inside the wound.

2. Put the sample in a container of alcohol (70% ethanol or isopropyl) — make sure they are fully covered.

3. Call the New Mexico Livestock Board right away: (505) 841-6161 or 505-414-2811

 

You can also report wildlife cases to New Mexico Game & Fish: 505-690-3208 and human cases to The New Mexico Department of Health: 833-796-8773

 

This is a reportable disease. If you see something, say something.

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TREATMENT (BEGIN IMMEDIATELY)

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• Remove all visible maggots and eggs.

• Kill larvae and eggs with alcohol, bleach, or formalin before throwing them away.

• Clean and treat the wound with a product like permethrin.

• Give an antiparasitic like ivermectin (ask a vet first).

• Continue wound care as needed.

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IMPORTANT UPDATES

As of May 2025, the U.S. has closed the southern border to cattle, bison, and horse imports due to the spread of NWS in Mexico. Agencies in New Mexico are preparing for possible cases and ask for your help in reporting and spreading awareness.

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RESOURCES (PDFs TO DOWNLOAD OR READ)

• Veterinary Guidance on New World Screwworm (PDF)

• NWS Awareness Letter from NM Livestock Board (PDF)

• NWS Poster: Life Cycle and ID (PDF)

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THANK YOU!

By learning about this threat and helping report suspected cases, you're helping protect animals, families, and communities across the Navajo Nation.

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